Hero's Son, Devil's Grandchild
by IllogicalEntity
Summary: The son of a hero, but the grandchild of a devil. Hunson Jacob Merten lost his parents (and his arm) at a young age. Swearing revenge, he went on a rampage killing anything and everything that got in his way. Only upon finishing his deed, did he truly realize what he had done, now he must meet with the legendary Prismo to fix the mess he's made. Small amount of Finn x Marceline.
1. A Broken Heart

**Chapter I**

 **A Broken Heart**

 _He stands there, surrounded by the fallen humans who dared oppose him. The blood on his hands, an even deeper red then the moon that night. His once blue eyes, now cold and dark as the shadows he cast, look upon the corpses lining the hilltop. The warrior took in a large breath, and laughed to the sky._ _ **"Finally, I have my revenge. Mark this night glob, for I killed them all single handedly! I, a warrior of human and demon blood has shown the people of this world the power I hold within my grasp! I, Hunson Jacob Merten, claim this planet as mine!"**_

He did it, he killed all of humanity single-handedly. Quite literally as well, seeing as his left arm was a mechanical replacement for the one he lost as a child. You might be asking, "Why the heck would somebody want to kill off all of humanity! He's part human himself!" You would be right to ask that question, but it is a long tale. So let's get started before this becomes an entire novel.

Over 100 years, the humans had once populated the land of Ooo. In the face of evils sprouted after the war, the humans had no choice but to escape to a different land. With the assistance of the vampire huntress Marceline, they were able to make it to a new land. A land with lesser evils, creatures that could be dealt with; and from there, humanity was able to start again. This did not change the fact that there were still beings on this planet, things beyond human imagination, the humans couldn't contend with. Just 17 years ago, the humans spotted a giant being in the sky right over Ooo trying to eat a comet whole! That was when they began a new project, a missile large enough to wipe out all of Ooo and the evil that lurked on it.

 **16 Years Ago**

 **The Land of Ooo**

Finn had turned 17 just under a week ago, and with that extra year Finn had grown just that much taller, leaner, and a little more mature (but not much). He was visiting his friend Marceline when they started discussing about how tall Finn got, well more so Finn pointed it out that he was now taller than her. Upon realization of this to be true Marceline took appropriate action and took Finn's hat and decided to keep it just out of his reach, floating near the ceiling of her living room.

"Okay, I get it! I can't fly, just give me my hat back." Finn said annoyed but amused at this little joke.

"Only if you agree to walk on your knees whenever you're in my house." Marceline responded in a teasing tone. She may look seventeen, but with her being over 1000 years old, she felt that she deserved a little more respect. Finn dropped down to his knees, chuckling to himself.

"There, happy now Marcy?" She returned the hat back to Finn, and flew back down on to the couch. Finn followed, and sat down opposite to her.

"Hey want to watch a-"Finn tried to speak but was interrupted when Marceline interjected. "Hey did something happen between you and Flame Princess? You two were acting kind of weird during your party, like you two trying to avoid each other."

Finn was quiet for a while, flustered by the suddenness of the question. Seemed like almost a full minute before he answered. "You know how FP and I dated a while back?" Marceline glared at Finn, knowing he was trying to stall as much as possible. "Yeah, you two were crazy about each other."

Finn sighed at the memory, then continued. "She's agreed to marry Cinnamon Bun. He's kind of had feelings for her for like a year now, and when bubblegum heard she thought it might be able to bring peace between the Fire and Candy Kingdoms. So now once she turns 17 in a couple of months, she's going to marry him." Finn frowned at the recollection of discovering this. He didn't sleep that night, and instead tried to clear his mind by going wolf chasing with Marceline.

"Ouch, sounds like it hurts." Marceline felt bad, she may have been curious but it didn't feel right making Finn sad like this. He might end up trying to distract himself by eating all her food again, and she was a bit low on cash at the moment. "Yeah, you have no clue… Hey got any food?" Marceline panicked for a moment.

"No!" She screamed, then after realizing her mistake lowered her voice down to a casual tone. "No, I don't have any food. Although, we could watch a movie if you're up to it." Finn thought on that for a moment, having forgotten that he was going to ask that same question before this down spiral of a conversation started.

"Sure, I'm going to make some popcorn. Don't choose anything lame, okay?" Marceline sighed with relief, and went through her old collection of films. After the popcorn was done, she was able to settle on an old classic. "Hey Finn, remember this?" She held up her copy of _Heat Signature_ , the same one that she, Finn, Jake, and a few of her old ghost friends tried to watch a couple years ago.

"Oh yeah, I forgot we left that here." Finn remembered back when she pranked them and convinced him and Jake they'd become vampires. "Pop it in!" They lied back on the couch on watched the mind-blowing masterpiece of a film.

They sat there the through the entire night, watching the movie, chatting, playing some music, usual bro-stuff. Finn finally noticed what time it was, and got up and headed for the door.

"Oh dang, I should probably get home. Jake's going to be worried if I'm not there." Marceline was caught off guard by this. "Why? Is Jake afraid of sleeping alone or something?" She knew the Jake was still kind of scared by her, but sleeping alone?

"Yeah, he's been afraid ever since the blank-eyed girl incident." Finn shuddered remembering that seriously bonked out day. He turned around to head home when Marceline suddenly grabbed his shoulder and turned him around.

"Wait Finn, why don't you stay with me tonight? Jake could use a little toughening up. Besides we haven't even had any REAL fun yet." Marceline was still looking for a bit of action tonight, after all even though it was fun, she's cooped up in her house all night. "I don't know…" Finn had to think for a while, but finally made his decision when Marceline mentioned going out for wolf chasing.

"Alright, let's head out!" Then with that, they ran outside in search of some wolves to chase. Where they ran, or in Marceline's case flew, all over the lands finding and chasing the wild wolves that populated the continent. When it became midnight, Finn stopped for a moment to sit down.

"Hey Finn, what are you sitting down for? They're going to get away!" Marceline gestured to the wolves who were taking advantage of this moment to flee. Finn looked up at Marceline then turned his head toward the sky.

"It's a little late," He yawned, and started to close his eyes. "And I'm so tired…" Finn fell backwards onto the ground and dozed off to sleep. Marceline sighed and picked up the hero and flew him back to his house.

'Big baby…' She thought to herself, 'Really big baby, seriously this is the last time I'm carrying him anywhere' Marceline grunted as she tried to get Finn's body in a better position to carry him, until finally she had his body nestled on top of her arms in the bridal position. 'He really has gotten taller than me, and…'

She mentally slapped herself before she was even able to finish the thought, I mean who is she thinking that he could actually be _cute._ Sure, she teases him about it from time to time, but she never really meant anything by it. Besides, Finn is obviously still hungover on Flame Princess.

By the time she finished that thought, she arrived at Finn's treehouse. She knocked on the front door, knowing Jake would be up as his "sleeping buddy" was not home. Jake slammed the front door open, with a panicked look on his face. He quickly took Finn's sleeping body and ran back in, not even acknowledging the fact the Marceline was there at all.

Then with that dealt with, she went back home and got some rest.


	2. Putting The Pieces Back Together

**Chapter II**

 **Putting The Pieces Back Together**

The hero awoke to the sound of his brother Jake singing in the kitchen, as the aroma of bacon pancakes filled his nose. He quickly got up and changed into his clothes and climbed down into the kitchen to join his brother in the singing their classic song 'Bacon Pancakes.' A couple minutes later, as they were finishing up their breakfast, Jake spoke to Finn.

"Hey dude, where you all last night? You know about our 'Sleeping Buddy System,' you never know if… _they_ will come back." Jake shuddered at the memory of those blank-eyed girls. "Dude, it's been a year since that. I don't think they're coming back"

"That's what they want you to think!" Jake peered into Finn's eyes, not appreciating his lack of concern as to the possible return of those… things. "And you didn't answer my question. Where were you?" Finn rolled his eyes at the dog, not believing the reaction Jake was having at his late arrival the previous night.

"I was out with Marcy last night. I swear, I'm pretty sure I saw at least like over half of the entire land of Ooo last night. By the time I fell asleep, I was so tired I could've slept for a whole day. That is, if we weren't having bacon pancakes for breakfast." Jake stared at Finn for a moment, making him uncomfortable.

"Jake, why are you staring at me? Do I have something in my teeth?" Finn immediately brought his finger up to his mouth, trying to search for some kind of embarrassing piece of food. "You've been spending a lot of time at Marceline's house recently. Can it be that you've finally moved on to someone besides Flame Princess?" Jake nudged his elbow against Finn, speaking to him in a teasing manner. Finn started choking on his last bit of food.

"No- *cough* dude, I'm not into Marcy." Finn drank his water and continued before Jake could make things any worse. "Listen if you want to know the truth, I'm messed up. Okay? Hearing about FP's marriage, its making me all messed up all over again. So, I go over to Marcy's place to, you know? Get away from the pain and stuff." Jake felt a sting of regret having heard this news.

"Woah, sorry bro. I didn't know it was making you feel this way." Jake comforted his brother, trying to think of a way to cheer him up. "Don't be sorry, I'm just… I'm just trying to figure things out." They sat for a couple minutes in silence until Jake thought of something to do.

"Hey, how about today we go to the Warrior's Rumble? We've been saving up to go see it, and you might even be able to compete if we're early enough." Finn thought on what Jake said for a moment. "Alright, let's go. I've been meaning to try out a new move anyway." Feeling a bit better, Finn packed some things and went out with Jake.

 **Two Hours Later**

"I can't believe how many people are going to be competing." Jake was looking at the list of competitors outside while Finn was registering. It was 12 in the afternoon, and the bustling crowd of people was starting to get more relentless. Trying to get into the colosseum-like building before the matches started, everyone was practically trampling one another with the hopes of getting a good seat.

"Ow, hey watch it bub!" Jake was shouting angrily at the people who kept on bumping into him. His patience was wearing thin, waiting for Finn. Over the mass of the crowd, Jake's ears finally picked up Finn's yells. Not wanting to deal with the crowd, Jake stretched to the size of a small house and walked over everyone towards the sound of Finn's voice. "Hey Jake, Over here!" He turned to his left and found his brother Finn standing next to a 1004 year vampire holding an umbrella over herself, Marceline the Vampire Queen.

"Marcy? What are you doing here?" Jake was confused as to why she would risk coming out in the afternoon. "Turns out she's been wanting to see the Warrior's Rumble for a while now." Finn was excited in being able to show off in front of Marceline, hoping to finally get a little more respect from her. "Yeah, the guy who organized this whole thing is an old friend of mine, so when I saw him mail me a free ticket I didn't want to waste it." Jake was shocked to hear about this.

"Wow, lucky you." He was also a little annoyed, his ticket was expensive as all hell. He probably would've said something else if Finn hadn't intervened. "The first match starts in 15 minutes, we should probably head in there now." Marceline and Jake agreed, thus all three of them headed towards the main building.

The Warrior's Rumble went on for hours, featuring some of Ooo's greatest fighters. Magicians, Trolls, Dragons, and Ninjas, there were so many people fighting it was like watching a war before your very eyes. Then when Finn made it to the final five, things were really getting interesting. Dodging and slashing with his sword, deflecting magic attacks from the lightning wizard, he appeared to be an unstoppable force. He never let up one bit on his opponents, sometimes switching from wielding his Finn Sword to dual wielding Finn Sword and his recently repaired demon blood sword.

However, what was most impressive was when it was just him and the massive ogre left. Finally being able to use out his new move (which he just copied from some old holotape he found under their treasure pile), he through his demon blood sword in the air catching the hilt horizontally in his mouth, held it in place with his jaw and brought out his grass sword. Using all three to slice his opponent three different ways in a single movement. Having been declared the winner, covered in sweat he raised his blades in triumph and smiled at the crowd cheering at him.

Meanwhile in the crowd, Marceline was watching awe-struck at what was happening in front of her eyes, and what was happening in her mind. She was amazed at what he was capable of after all this time, to the point where for a moment. _Her heart fluttered_ … 'Damnit Marcy, don't go into that again. It isn't real.' Marceline was confused at what she was feeling, she didn't want anything to happen between her and Finn, romantic or otherwise.

After the cheering had subsided and Finn had left the arena, everyone started leaving. "Man I can't believe it, well actually I can because it's Finn for crying out loud. But did you see that move! He was all like SLICE and CHOP and-" Jake kept going on and on about how Finn did in the match, but for the most part Marceline was blocking him out. She was trying to figure out what was going on with her. "That lightning wizard just kept shooting and shooting but Finn was all like NOPE, then-" At this point Marceline had finally snapped, cursing at herself for letting herself develop these feelings. "Shut Up!" She was screaming at herself, but Jake fortunately thought she was speaking to him.

"I'm sorry Marcy, I didn't mean to annoy you." Jake shivered a little, obviously still a little scared of her. Marceline realized what happened, recovering from her inner battle. "Oh, no I wasn't talking to you." Jake was confused, but still didn't go any farther about the brawl until they met up with Finn outside.

"Congrats bro! I knew you had it in you!" Jake ran toward his friend with open arms and threw himself against him, and afterwards started recalling the events of the brawl again. While Finn was listening to Jake go on about his fight, he noticed Marceline staring at him. "Marcy, what are you staring at?"

Having to recover again, she shook herself out of it. "Nothing, just looking into your deepest fears." Finn, trying to turn things around, joked a little. "Notice how there's nothing there." Finn actually felt proud enough to laugh at his own joke for a moment.

Marceline playfully hit Finn's shoulder trying to see how the back of her mind would react if she tried it. She actually found that she… _like it_. "Ow, let up. I literally just fought 120 men, cut me a little slack on the punches." Finn complained. Marceline wanted to get away from this part of her head and tried to get a little more involved in the conversation.

"90 men and 30 women actually, a little unbalanced if I say so." The three of them came to a split in the road, realizing they had to part ways now. "Well, see you later Marcy." Finn and Jake said their goodbyes and started toward their house, but Marceline didn't want to go to her house. If she did, then her mind would wander. Eventually it would wander to this place of potential romantic involvement.

"Hey wait guys, mind if I come over? I don't really have anything to do." Finn and Jake agreed and headed off toward the house for some lunch and BMO. While she floated close behind, she overheard Jake talking to Finn about her. "Looks like things are getting serious between you two, going over to each other's houses." He was still teasing Finn, trying to get a better reaction out of him than the one this morning. Of course, because of how Marceline's been lately, she panicked and for a moment thought that possibly Jake knew something.

"Jake, stop. You know there's nothing going on between me and Marcy." Finn tried to get the dog to stop, but he kept teasing. "What can I do to get you to stop it?" Finn whispered angrily to Jake as he opened the door to their treehouse. Marceline went up to the living room while the two boy's wen to the kitchen to make some snacks.

"*cough* lovebirds *cough*" Jake was still teasing him when he finally snapped. "Damnit Jake! What do I got to do to make you stop that!" Marceline overheard that part and started towards the kitchen but stopped when she heard Jake comply.

"Alright, I'll stop. But you know, you have to have realized that she is pretty for a terrifying undead chick." Jake finally let up, but was still trying to get something out of Finn. He was hoping that Finn could say something that he could use to get him off of FP. "Fine, she is kind of pretty. Maybe even sexy…" Finn paused for a good while. Jake was relieved he finally got him away from any thoughts of Flame Princess, but a little worried. What would happen if it turns out he accidentally just set up his brother up with a terrifying human-demon-vampire hybrid?

"Okay, she's sexier than your #1 Dad mug. I admit it, but I don't see it going anywhere. I mean sure, she's cool and likes to hang out with me. Then there's the whole her being technically half human which is nice. But she's over 1000 years old, that's an even bigger age gap then between me and princess bubblegum, and she's over 800 years old! Not to mention, she's immortal. I have a fixed lifespan, I age, and she doesn't. Imagine if we actually ended up together, what if we end up being together so long she has to watch me die. It wouldn't be right."

Jake was relieved to hear he in fact didn't set up Finn and Marcy, but she heard everything. She couldn't help feel both glad AND disappointed that Finn couldn't see them being together. She drifted back over to the couch and started playing on BMO. She sat there trying to beat the same level for a minute until Finn and Jake came out with a plate of chips and red salsa. They chose a different game on BMO and played until it was late out.

"Hey Marcy, we still have one of PB's liquid pyrotechnic firework things left over. Want to go up to the roof and fire it off?" Finn was getting bored the game and Jake's thumbs were starting to get sore. Marceline thought on it for a couple of seconds before answering. "Sure, that'd be nice" Finn headed up with Marcy while Jake went to go get the rocket. The full moon was out tonight, lighting up the treetop well enough so that they could find the blanket that the boys keep up there.

"Hey Finn, you really think I'm sexy?" Marceline regretted saying that the moment it left her mouth, she could feel a grayish blue blush rise in her face. The question totally caught Finn off guard, causing him to lose his footing for a moment. After he caught himself he answered, "I didn't know you heard that. Listen I'm sorry if I said something that you may have not wanted to hear." Finn was rubbing the back of his neck, his face plastered with embarrassment.

"No, you didn't say anything I didn't hear anything I didn't want to know, I just… I didn't know YOU thought I was you know, all that stuff you said." Marceline was getting bluer and bluer from the embarrassment. "You know, maybe it could work out. Just like a short, sweet little thing." Finn was shocked by the statement he just said, and it was obvious that Marceline was too.

"Maybe, yeah… That could actually work, keeping it from going for too long." Marcy was actually agreeing, willing to go out on a limb and try this. "So, you want to like… go on a date sometime?" Finn was wondering about how he should go about things with her, I mean he's been on dates with FP before but he doesn't really know what to do in this situation. From this point onward is it like, what would they even do for dates? Should they just keep doing what they've been doing, bust with maybe a hug and a kiss here or there? He really didn't know, so he went out on a limb and tried kissing her.

It was a perfect situation, on the rooftop of the treehouse, the full moon was out, in a moment there going to fireworks whether this worked out or not. A kiss at this moment just seemed to go nicely with their now pronounced interest in each other. So when Finn's lips pressed up against hers, it felt nice, good even. Just standing there on the roof top, kissing a boy who she liked and wouldn't be like her ex, ash. If only Jake wasn't watching when this happened, realizing that his worst fear and just come alive.


	3. A Missing Arm

**Chapter III**

 **A Missing Arm**

Now they may have not expected it to last for long. However the relationship they'd created only grew stronger and stronger as time had passed. For a little over a year they dated, until Finn proposed to her on that same rooftop. Then a year later they had a little boy which Finn thought they should name after Marceline's father, Hunson Abadeer. Marceline was resilient about it, but agreed on the condition that her father was never allowed to meet their child. And so, the Hero of Ooo and the Vampire Queen had a child, Hunson Jacob Merten. The three of them and all of the land of Ooo lived in peace (except for the occasional monster attack which were quickly stopped by our Hero, Finn the Human), until that fateful day.

The humans that had escaped from Ooo all those years ago had finally finished the weapon. It was only five years after the birth of Hunson Merten when they launched the missile. The people of Ooo was unaware of the impending weapon until there was only an hour until impact, with the sudden threat approaching, mass panic ensued. Chaos as people quickly tried to stock on food, water, and other basic necessities before heading into the bunkers.

Finn and Marceline were prepared, for Finn had built an underground bunker near the treehouse back when the crazy storm popped up 8 years ago, and it was only minutes away. They quickly took Hunson and flew over (Marceline had to carry Finn), to find Jake, Lady Rainicorn, their kids, and BMO all heading into the bunker. Unfortunately there was also some less-than-desirable people head towards the group as well.

It appeared to be a group of looters, they've been popping up everywhere since everyone learned of the impending doom. "Stop them!" The leader of the pack was trying to keep the supplies inside the bunker to him and his pack, unfortunately he was unaware of who they were up against.

"You take Hunson into the bunker, I have to keep these guys from hurting anyone." Finn handed the child to Marceline as she dove into the entrance. The bunker was a bit roomier that Marceline had expected, and the walls were made from wooden boards. The support beams were made from some weird metal that only held up additional beams. The bunker didn't seem like much but they were too far away from another bunker that this was their best option.

"Are you sure this'll be safe Finn?" Marceline was nervous about the possibility of something happening to her son, but then she heard Finn's scream. In a sudden panic, she flew outside to find her husband on the ground. He was bruised and cut in many places, but he was still fighting. 'That's right, he left his swords at home.' Marceline realized what needed to be done, she flew off towards the gang of looters to ward them off.

"No Marcy, go into the bunker! Keep an eye on Hunson!" Finn shouted at Marceline over her rash decision. "I'm not leaving you out here alone!" But just as she said that, several miles away, the missile hit. With the sudden realization that there was so little time left, everyone stopped fighting and headed towards the bunker. It was too late, the shockwave from the impact passed by, and everyone was blown away. There was a painful, searing hot sensation, then nothing. Everyone in the bunker felt the shockwave through the entire room around, the support beams started falling.

"NO!" Hunson screamed as he watched his parents die, only to get cut off by the sound of the falling debris of the ceiling. He lied there, unable to move. The pain he felt from the collapsed bunker was almost eclipsed by the pain of watching his parents die before his eyes, almost. He tried to move, but was stopped by a sudden burst of pain from his left arm. He looked over and saw… nothing. His shoulder had a support beam in it, going straight through the front shoulder and sinking into the ground below it. After just a second of the sight, he fell unconscious. Jake and Lady were pretty good, considering the situation. Jake heard Hunson stop screaming.

"Hey! Kiddo, you okay?" He screamed through the rubble. Scared when he didn't hear a response, he stretched his body through the wreckage until he found his body. "Lady, look the first aid kit! Hunson's not doing so good" Jake grabbed Hunson's body and waited till she found the first aid, then with the both of them in hand he stretched out of the bunker, through the ground and placed Hunson on the clearing Jake had made.

The three of them were surrounded by miles and miles of scorched dirt, what used to be a luscious grassland was now a barren wasteland. 'Who could've done something like this?' Jake thought to himself. While he shrank down to normal size, he spotted two figures among the wreckage, Finn and Marceline. He ran over to check on them, but what he saw sickened him to the bone. Finn was dead, blood running out his nose, mouth, and ears, splintered remains of the old treehouse were going through his entire body. Marceline was in better shape, but with a broken off branch through her chest. She was dead as well…

"Oh crap, what am I going to tell Hunson?" Jake mumbled to himself as he turned around and saw him awake, staring at his parent's bodies. Hunson's eyes started watering, tears leaking out of his eyes. His parents were dead and his arm was most likely gone forever, he was all alone. Despite the pain he was in, he started crying, wailing, and screaming to the heavens. 'Who did this? Why did they do this? Where are they?' Hunson asked himself so many questions. He wanted his parents to be alive, he wanted to have his arm, he wanted to go back home and find his mom and dad cooking dinner. He wanted revenge, he wanted to find the people who did this. He wanted to make them pay.

'Mark this day glob, this day I swear that I'm going to kill whoever did this.' Hunson swore to himself, to his parents, to glob himself.

This is what started the legacy of what was soon to be called ' _Hell's Decent.'_ Why Hunson Jacob Merten killed all of humanity. After getting a replacement arm from Princess Bubblegum, he began his training to exact his revenge. By the time he was seven, the first humans arrived on Ooo. Caught off guard by the discovery that the humans weren't extinct, everyone crowded around the shore were the humans had arrived. This proved to be a mistake, as the humans took this as an opportunity to start mowing down the people where the stood.

Witnessing the massacre in front of him, Hunson quickly ran to the front. The humans ceased fire, as they assumed Hunson was a human. Little did they know, his demon blood made him a dangerous enemy, especially since they were shooting down his friends. "Come over here sonny, get away from the monsters. Qui-" Hunson lunged forward and shoved his hand through the soldier's chest, coming out the other end. He held the man's heart, stared into his victim's eyes and sucked his soul out through his mouth.

He discovered his parent's killers, _the humans_. With the cunning of a human, the power of a devil, and the abilities of a vampire, he was able to dominate the small army. Before the people of Ooo could recover from the shock of that seven year old, little boy killing a man in cold blood, the battle was over.

* * *

But this was merely the beginning of a journey that would lead to him killing every human on this miserable planet. We're here to talk about the end of his journey, maybe one day I'll go into more detail about his journey into the pits of hell. But today is not that day, today is when we finally talk about what he's going to do next. Actually, realizing how long this chapter's already gotten I'm actually going to make that tomorrow. Crap.


End file.
